Abstract

During the DRIVE (Diurnal and Regional Variability of Halogen Emissions) ship campaign we investigated the variability of the halogenated very short-lived substances (VSLS) bromoform (CHBr3), dibromomethane (CH2Br2) and Me iodide (CH3I) in the marine atm. boundary layer in the eastern tropical and subtropical North Atlantic Ocean during May/June 2010. The highest VSLS mixing ratios were found near the Mauritanian coast and close to Lisbon (Portugal). With backward trajectories we identified predominantly air masses from the open North Atlantic with some coastal influence in the Mauritanian upwelling area, due to the prevailing NW winds. The max. VSLS mixing ratios above the Mauritanian upwelling were 8.92 ppt for bromoform, 3.14 ppt for dibromomethane and 3.29 ppt for Me iodide, with an obsd. max. range of the daily mean up to 50% for bromoform, 26% for dibromomethane and 56% for Me iodide. The influence of various meteorol. parameters - such as wind, surface air pressure, surface air and surface water temp., humidity and marine atm. boundary layer (MABL) height - on VSLS concns. and fluxes was investigated. The strongest relationship was found between the MABL height and bromoform, dibromomethane and Me iodide abundances. Lowest MABL heights above the Mauritanian upwelling area coincide with highest VSLS mixing ratios and vice versa above the open ocean. Significant high anti-correlations confirm this relationship for the whole cruise. We conclude that esp. above oceanic upwelling systems, in addn. to sea-air fluxes, MABL height variations can influence atm. VSLS mixing ratios, occasionally leading to elevated atm. abundances. This may add to the postulated missing VSLS sources in the Mauritanian upwelling region. [on SciFinder(R)]